Contacts are utilized, among other things, to provide connections between a transistor region of a semiconductor die and an interconnect metal layer situated above the transistor region. To achieve high circuit density, these contacts, which generally have a high aspect ratio, must fit within a small area of the semiconductor die without touching or otherwise interfering with each other. As such, it is important to control contact hole width during contact formation to achieve a contact having a sufficiently small width.
During a conventional contact fabrication process, a contact hole is typically defined by lithography and etched in an oxide layer, which can be situated, for example, over a transistor region of a semiconductor die. The resulting contact hole can be formed over a silicide layer, which can be connected to, for example, a source or drain area in the transistor region of the semiconductor die. The contact hole is then lined with a barrier layer comprising a metal, such as titanium, and filled with a metal, such as tungsten, to form a contact. However, before the barrier layer can be deposited on the sidewalls of the contact hole and on the silicide layer situated at the bottom of contact hole, a native oxide layer that forms over the silicide layer must first be removed. In the conventional contact fabrication process, the native oxide layer is typically removed by utilizing a sputter etch process comprising argon.
However, during the sputter etch process, top corner portions of the oxide layer than defines the contact hole are also etched in addition to the native oxide layer, which causes the top of the contact hole to increase in width. As a result, the contact that is formed after the contact hole has been filled with tungsten has an undesirable increased width compared to the initial width of the patterned contact hole.
Thus, there is a need in the art for a method for forming a contact over a transistor region of a semiconductor die that prevents an undesirable increase in contact hole width during contact formation.